1. Field of the Invention
The present invention relates to an absorbent fibrous web. Specifically, the present invention concerns an absorbent fibrous cellulosic web possessing improved integrity.
2. Description of the Related Art
Absorbent structures for the absorption of body fluids are known to those skilled in the art. As a general rule, such structures comprise a water-impervious backing sheet, an absorbent fibrous web, and a water-pervious body-side lining material. The fibrous web is sandwiched between the body-side liner and the backing sheet. The fibrous web is suitably formed from cellulosic material such as wood pulp fluff, cotton, rayon, and the like. Unfortunately, due to stresses placed on such fibrous webs during use, the webs have a tendency to separate into clumps of material. This is particularly true when the absorbent fibrous webs are wet. This clumping results from a tendency of the fibrous webs of cellulosic material to possess a relatively low degree of structural integrity. That is, the fibers of the web tend to separate easily thus allowing the webs to pull apart.
Means of enhancing the structural integrity of cellulosic fibrous webs are known. For example, U.S. Pat. No. 3,903,890 issued Sep. 9, 1975 to Mesek et al., is directed to a disposable diaper of simple construction. Mesek et al., describes improving the structural integrity of a fibrous web by applying a binder material to a surface of the fibrous web opposite a water-impermeable backing sheet. The binder material extends through the web thickness in spaced linear areas. The binder described may be either thermoplastic or thermosetting, and is preferably in the form of an aqueous emulsion or latex.
U.S. Pat. No. 4,573,989 issued Mar. 4, 1986 to Karami et al., is directed to a disposable diaper and method of manufacture. This reference describes spraying a binder between an absorbent fibrous web and a water-impervious backing sheet. The binder penetrates the fibrous web to adhere the web to the backing sheet. The presence of the binder material is described as rendering the pad highly tear resistant.
U.S. Pat. No. 3,978,257 issued Aug. 31, 1976 to Ring is directed to an internally adhesively bonded fibrous web. The web described by Ring has an adhesive uniformly disbursed in the X-Y direction of a fibrous web. The adhesive is not uniformly disbursed in the Z direction and is located primarily in an internal plane of the fibrous web. Thus, both outer surfaces of the web are generally adhesive free.
Unfortunately, as a general rule, when adhesives are used as described in the above references to enhance the structural integrity of a fibrous cellulosic web, the increase in integrity causes a decrease in the degree of softness or suppleness of the web. Obviously, when the fibrous webs are intended for use in products such as diapers, it is desirable that the fibrous web be highly supple, thus, increasing the comfort to a wearer. If the adhesive is not carefully selected, the adhesive may provide satisfactory structural integrity when the fibrous web is dry, but fail to provide desirable structural integrity when the fibrous web is exposed to a body fluid such as urine. Additionally, if the adhesive is hydrophobic in nature, application of the adhesive may deleteriously affect the absorbent characteristics of the fibrous web.
Accordingly, it is desirable to provide a fibrous web which possess both a high degree of wet and dry structural integrity and which maintains its absorbency and suppleness in both the dry and wet state.
Polymer complex formation between water-soluble polymers has been described. See for example, K. L. Smith et al., Industrial and Engineering Chemistry, 51 (11), 1361, (1959); Y. Osada, Journal of Polymer Science: Polymer Chemistry Edition, 17, 3485, (1979); S. K. Chatterjee, et al., Die Angewandte Makromolekulare Chemie, 116, 99 (1983). Polymer complex formation between water-soluble polymers generally results from the formation of extremely stable hydrogen bonds between the polymers when the polymers are in contact in an aqueous solution. In particular, poly acids, such as poly (acrylic acid) or poly (methacrylic acid), are reported to form complexes with polyethers such as poly (ethylene oxide) and polyamides such as poly (vinylpyrrolidone) or poly (ethyl oxazoline).